1. Field of the Invention
The present invention relates in general to the field of microprocessors, and in particular to allocation of reservation station entries in a microprocessor.
2. Description of the Related Art
In the issue queue design of today's microprocessors, a reservation station is normally used to store the operands of an instruction along with the opcode. Typically, each issue queue entry contains an instruction opcode and the operands associated with the instruction. For example, for a fixed point instruction containing two operands, each issue queue entry will have two operands included with it. Since each operand can be 64 bits wide, each issue queue entry will need a reservation of 128 bits (i.e., 2×64 bits) to contain the operands. In conventional designs, two operands are reserved in a reservation station for an instruction, even when an instruction (such as a fixed point instruction) may need less than two operands. Typically an issue queue of depth N will need a reservation of depth 2N to support it. For a large issue queue, the number of bits kept in the reservation station can be prohibitively large, and the reservation station can consume a lot of power.